1. Field of the Invention
The invention relates to a radial piston pump having a plurality of pump elements in a pump housing arranged substantially radially around an eccentric shaft whereby the pump elements have an inlet valve and an outlet valve activated by the medium that is to be pumped, and whereby the inlet valves and outlet valves are each disposed at the outer side of the pump elements that faces away from the eccentric shaft and whereby the inlet valves are each arranged, in their flow-through direction, in a continuous extension of the cylinder bore of the pump element substantially coaxial relative to the pump piston, and whereby all inlet valves are connected to a joint intake channel that leads around the outside of the pump housing.
2. The Prior Art
Radial piston pumps in the simplest construction, as they have been used for some time in small electric-powered hydraulic units for actuation of vehicle tops or the like, independent from the driving motor, are operated without valve control, which keeps structural requirements at a minimum but which allows only a low degree of efficiency. In addition to the unfavorable pressure conditions in each individual pump element, which is caused by control adjustments of each individual pump element, there is noise created in the entire interconnected hydraulic system as a result of pressure pulses, which is undesirable and disturbing.
For example, radial piston pumps have been made known in DE 197 26 572 A1, DE 197 25 563 A1 or also DE 197 25 564 A1 wherein an automatic check valve is provided on the inlet and outlet-side of each pump element, which increases the degree of (operational) efficiency of these pumps as they are used as high-pressure fuel pumps in so-called common-rail injection systems of combustion engines and which in turn lowers the operating noise. However, a disadvantage in these known arrangements are the large dead spaces or (cylinder) clearance caused by the arrangement of the valves as well as the relative complicated structural design, which increases costs in manufacturing, assembly and maintenance and which also increases breakdowns.
Furthermore, from WO 99/19621 there has been made known a radial piston pump of the type mentioned above, for example, wherein the inlet valves and the outlet valves are arranged respectively on the outer side of the pump element and whereby the inlet is arranged in its flow-through direction substantially coaxial relative to the pump piston, and the outlet valve is arranged in its flow-through direction substantially parallel and off-set relative to the eccentric shaft. In contrast to the above-mentioned known arrangements in which the inlet valve is arranged on the inner side of the pump elements facing the driving eccentric shaft and the outlet valve is arranged at the outer opposed side of the pump elements facing away--whereby over the entire length of the pump elements a dead space is created that influences the degree of efficiency negatively, which is caused by the always present residual elasticity of the medium to be pumped the two valves, which are necessary for the functioning of the pump, are now disposed on the same outer side of the pump element, which in turn makes possible a decrease of this dead space and thus an increase in the degree of efficiency.
A disadvantage of this known arrangement, which is designed for high-pressure fuel supply, especially in the above-mentioned common-rail injection systems with operational pressures of 1,000 bars or more, is mainly the necessary requirement to deal with these high pressures in view of dependable tightness, special construction or arrangement of valves, threaded joints, seals etc. For the hydraulic use mentioned in the beginning, particularly in the area of actuation of the vehicle tops or the like, at which operational pressures of the hydraulic medium in the range of approximately 20-40 bars are quiet sufficient, other criteria are in the foreground--specifically one should mention here the simple and cost-effective design, easy assembly and maintenance and the like.
Pump elements designed as complete units are generally known from DE 197 32 748, for example, but they are not intended for radial piston pumps with their necessary characteristic features. In addition, these pumps elements are not designed as more operationally dependable units and units that are easy to be dismantled since they are pressed into the cylinder bore of the pump housing and may only be removed by damaging the same. Finally, there are no indications in DE 197 32 748 to insert pump elements into bores that are interconnected by a surrounding joint inlet channel.
Such a joint inlet channel is in deed known from EP 304 750 A1, but it is not designed as a groove surrounding the pump housing and it is designed whereby its covering is not an attached sealing member that is separate from other housing components and whereby it is not assembled independently relative to the assembly of the actual pump housing.
It is the object of the present invention to improve a radial piston pump of the type stated above in such a manner that the mentioned disadvantages of the known arrangement of this type are avoided and that particularly a more simplified, flexible and operationally dependable design is made possible with a high degree of efficiency and low noise emission.